Generally, residential telephone service is provided via a central office telephone line which electrically connects a residence to a central office switch. This connection, which is usually made to the residence at a location known as the protector block, enables a residential telephone to be used to communicate with others via the central office switch. Typically, multiple telephones, referred to as extensions, are located throughout the residence and are all individually electrically connected to the protector block (i.e., a "home run" connection) or are connected to each other (i.e., "parallel" connection). Thus, any one of a plurality of extensions located in, for example, the kitchen, living room, family room, study, bedrooms, basement, garage, or workshop, can be used to answer incoming calls from others or initiate outgoing calls to others, via the central office telephone line. Multiple extensions are desirable because they provide easy access to answer or initiate telephones calls, regardless of a person's location in the residence.
Electrically connecting multiple extensions to a central office telephone line causes all such extensions to ring to indicate the presence of an incoming call. In this regard, an extension's ringer is driven by a nominal voltage, usually 86 volts rms at 20 hertz, superimposed temporarily on the central office telephone line by the central office switch to indicate the presence of an incoming call. It is sometimes undesirable to ring all extensions in a residence when an incoming call is received, including for example, ringing an extension in a child's bedroom when the child is studying; or ringing a extension in a bedroom when a family member is asleep. Further, it is sometimes undesirable to ring all extensions during certain times of the day when persons within the residence tend to congregate in particular areas of the residence, including for example, ringing bedroom, study, workshop extensions, during times when family members are likely to be eating dinner in the kitchen; or ringing bedroom, workshop, kitchen extensions during times when the only family member present is likely to be in the study.
Electrically connecting multiple extensions to a central office telephone line also allows all such extensions to be used to initiate an outgoing call, via the central office telephone line. In this regard, any extension can be used to initiate an outgoing call by taking the extension's hand set off-hook to obtain central office dial tone and dialing a number sequence corresponding to a called party's telephone number. It is sometimes undesirable to allow multiple access to the central office telephone line by all the extensions, including for example, allowing an extension in a child's bedroom to be used to initiate an outgoing call during times when the child should be studying.
Electrically connecting multiple extensions to a central office telephone line also allows such extensions to access the central office telephone line when another extension is in-use, i.e., presently being used to engage in an ongoing call. Consequently, the possibility arises that a second user may disrupt a first user's ongoing call by attempting to initiate an outgoing call at another extension. For example, a second family member may disrupt a first family member's ongoing call by taking an extension's hand set off-hook and attempting to dial a telephone number, without realizing that the first family member is already engaged in a call.
Typically, residential telephone service is used for voice calls. However, residential telephone service is increasingly being used for data calls, i.e., data transmissions and communications between machines including, for example, facsimile machines and computers. In this regard, it is becoming more common for a central office telephone line to be electrically connected to, for example, a computer for the purpose of allowing a user of the computer to navigate the Internet, send or receive e-mail messages, or send or receive facsimiles. Providing multiple extensions within a residence raises the possibility that a data call at one extension may be appreciably disrupted by an attempt to initiate an outgoing call at another extension. For example, a second family member disrupting, e.g. disconnecting, a first family member's facsimile transmission by taking an extension's hand set off-hook and dialing a telephone number, without realizing that the first family member is engaged in a data call.